Stator assembly



July 28, 1964 M. B oB ETAL. '3,142,475 l sTAToR ASSEMBLY Filed Dec. 28, 1962 jm?. REW.-

United States Patent 3,142,475 STATUE ASSEMBLY Melvin Bobo, Topsfield, .lack Reid Martin, Bedford, and Robert John Smuland, Reading, Mass., assignors to General Electric Company, a corporation of New York Filed Dec. 2S, 1962, Ser. No. 248,071 6 Claims. (Cl. 253-78) This invention relates to stator assemblies for iluid ow machines such as turbines and compressors and, more particularly, to an improved turbine nozzle diaphragm or other stator assembly subjected to substantial changes in temperature during normal operation. The invention also relates to the support of such stator assemblies.

An annular nozzle diaphragm is conventionally positioned between the combustor and the turbine wheel of a gas turbine engine for directing the high temperature products of combustion to the turbine wheel. The nozzle diaphragm has dual functions, the first being to convert the high pressure products of combustion supplied by the combustor into a high velocity iluid stream and the second being to direct the high velocity stream against the turbine wheel at the proper angle. The effective force of the iluid stream on the turbine wheel is related to both the velocity and the angle of the fluid stream. Therefore, the forces exerted on the turbine wheel by the fluid stream will be equal about the entire periphery of the wheel only if the fluid stream is supplied uniformly by the nozzle daphragm. When non-uniform forces are exerted on a turbine wheel about its periphery, the wheel is said to be subjected t excitation forces. As the turbine wheel rotates, the individual buckets are subjected to pulsating forces which cause undesired vibrations and stresses. If sufficiently severe, these excitation forces can cause the turbine wheel to fail. It is therefore extremely desirable to direct the fluid stream against the turbine wheel such that uniform forces are exerted about the entire periphery of the wheel. This can be done by making all of the flow areas between adjacent vanes of the nozzle diaphragm the same at the normal operating temperature since the local force of the fluid stream is determined by the flow areas.

In practice, however, this has not been easily accomplished in the past. One structure having the desired equal ow areas is a nozzle diaphragm formed and supported as a complete integral ring having equal flow areas between adjacent vanes. This integral structure may not, unfortunately, always be a practical one in view of the temperatures to which the nozzle diaphragm is subjected during turbine operation. These temperatures are customarily around l800 F. but may even be substantially greater. Because of the thermal stresses which would otherwise be encountered at these temperatures, the nozzle diaphragm is often segmented and mounted with the segments in circumferentially spaced relationship in order to permit expansion and contraction in response to temperature changes. The ,segments of such a nozzle diaphragm expand as the diaphragm approaches its operating temperature, the end vanes of adjacent segments moving toward each other, thereby reducing the flow area therebetween, while the adjacent vanes within the individual segments are moving apart so as to increase the flow area therebetween. The diiculty of obtaining equal flow areas at the nozzle diaphragm operating temperature of 1800 F. or higher will thus be appreciated.

Consequently, in view of the difficulty in obtaining equal ilow areas, it has often been the practice to operate with unequal areas along with accompanying excitation forces provided, of course, that the excitation forces are within acceptable limits. For example, the nozzle diaphragm may be fabricated as a complete integral ring structure having equal How areas between adjacent vanes. The dia- .3,142,475 Patented July 28, 1964 ICC phragm is then cut into segments, and the segments are mounted in the gas turbine engine with spaces between adjacent segments. The diaphragm segments expand into abutting relationship when the diaphragm is at its normal operating temperature, the abutting relationship being desirable in order to reduce leakage at the operating temperature. When such a nozzle diaphragm is at its normal operating temperature, the areas between the end vanes of adjacent segments are smaller than the areas between the other vanes, the amount being determined by the width of the material removed when cutting the ring into segments.

Under certain circumstances, however, the excitation forces accompanying unequal areas cannot be tolerated. Therefore, diaphragm structures must be provided which have equal areas between all adjacent pairs of vanes at the normal operating temperature of the nozzle diaphragm. This may be accomplished by fabricating a complete integral ring structure as above, the vanes being unequally spaced, however, so as to form unequal areas between adjacent vanes. The nozzle diaphragm is then cut into segments, and the segments are mounted in the engine as described above. The unequal areas between the vanes compensate for the width of the sawcuts such that all flow areas are equal at the normal operating temperature of the nozzle diaphragm. Such nozzle diaphragm structures are difficult and expensive to manufacture because of the necessity to unequally space the vanes.

It is therefore a primary object of this invention to provide an improved stator assembly having equal areas between all vanes at its normal operating temperature.

Another object of this invention is to provide an irnproved nozzle diaphragm or other stator assembly having equal areas between all vanes which is relatively easy and inexpensive to manufacture.

A further object of this invention is to provide an improved method of supporting a segmented nozzle diaphragm or other stator assembly such that the ow areas between all vanes are equal at the normal operating temperature.

Briey stated, in accordance with the illustrated embodiment of the invention, a nozzle diaphragm is formed of a plurality of nozzle diaphragm segments, the segments being fabricated individually in accordance with conventional manufacturing techniques. Each of the segments is comprised of arcuate inner and outer shroud members and a plurality of vanes radially positioned therebetween, the shroud members extending circumferentially beyond the end vanes of the segments. The lengths of the extensions are such that the ow area between the end vanes of two abutting segments is equal to the flow areas between adjacent vanes of the individual segments at any temperature. The individual diaphragm segments are expansively supported in the engine in circumferentially spaced relationship such that the segments expand into abutting relationship at the normal operating temperature of the nozzle diaphragm. At the normal operating temperature of the nozzle diaphragm, the flow areas between the end vanes of abutting segments are thus equal to the areas between adjacent vanes of the individual segments.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter regarded as the invention, it is believed that the invention, together with further objects and advantages, may best be understood by reference to the following description taken in connection with the accompanying drawing in which:

FIGURE l illustrates in cross section a portion of the nozzle diaphragm of this invention, the diaphragm being shown mounted in a gas turbine engine;

FIGURE 2 is a View, partially cut away, of the nozzle 3 diaphragm of FIGURE 1, the view being taken along line 2-2 of FIGURE l;

FIGURE 3 is an illustration in cross section of one of the nozzle diaphragm segments, the segments being cut along line 3-3 of FIGURE 1; and

FIGURE 4 is a view taken along line 4-4 of FIGURE 1 which illustrates the spacing between adjacent vanes of the nozzle diaphragm.

Referring first to FIGURE l, a portion of a gas turbine engine is illustrated, the engine having an outer cylindrical casing comprised of annular sections 11 and 12 secured together at the flanges 13 and 14 by cireurnferentially spaced bolts 15 as illustrated or by other suitable fastening means. An annular combustion space indicated generally by 16 is defined between the casing 10 and an inner wall 17. The inner wall 17, a stationary member having support capability, may be, for example, an annular iange extending axially from the rear frame of the compressor (not shown). An annular combustion liner 15 is located within the combustion space 16, the liner 18 having suitable openings therein (not shown) through which high pressure air supplied by the compressor to the combustion space 16 can flow to support combustion in the interior 19 of the liner 18.

An annular nozzle diaphragm indicated generally by 20 is located at the aft end of the combustion liner 18 for supplying the hot products of combustion to a row of turbine buckets 21 at the proper velocity and at the proper angle. The nozzle diaphragm 20, along with its construction and mounting, forms the basis of this invention and will be described in detail at a later point in this specification. The turbine buckets 21 are peripherally mounted on a turbine rotor wheel 22 which, along with its associated shaft 23, is rotatably mounted within the casing 10 by suitable mounting means not illustrated. Now that the nozzle diaphragm 20 has been located with respect to the other turbine structure and its general functions with respect to such other structure have been pointed out, the invention itself will be described.

As pointed out previously, the flow areas between all vanes of a nozzle diaphragm should be equal so that the products of combustion will be supplied to the turbine buckets at a uniform velocity about the entire periphery of the diaphragm. In order to provide the desired equal areas at its normal operating temperature, the nozzle diaphragm 20 is comprised of a plurality of segments 25 as shown by FIGURE 2, one of the segments being illustrated by FIGURE 3. Referring now to FIGURES 1-3 in particular, each segment 25 is independently formed as an arcuate segment. Each diaphragm segment 25 is comprised of an arcuate outer shroud member 26, an arcuate inner shroud member 27, and a plurality of vanes 28 radially positioned between the shrouds 26 and 27 and secured thereto, the vanes 28 having leading edges 29 and trailing edges 30. An arcuate circumferentially extending flange 31 projects radially outwardly from the outer shroud member 26 adjacent the trailing edges 30 of the vanes 28. A similar flange 32 projects inwardly from the inner shroud member 27. An opening 33 is provided in the flange 32 at the circumferential center of each segment 25, and openings 34 and 35 are circumferentially spaced on opposite sides of the opening 33. If desired, openings 34 and 35 may be made larger thany opening 33 as illustrated; the reason for the difference in size will soon become obvious. Plates 36 and 37 are provided on one end of the outer shroud member 26 and the inner shroud member 27, respectively. The plates 36 and 37 extend c1rcumferentially beyond the end of shroud members so as to overlap the shroud members of the adjacent segment 25 when the segments 25 are mounted in the engine. The plates 36 and 37, discussed in detail at a later point 1n this specification, reduce leakage.

Turning now to FIGURES 2-4, each segment 25 of the nozzle diaphragm 20 is formed as an exact 60 segment by conventional manufacturing techniques. The segments 25 may, for example, be fabricated from sheet metal brazed or otherwise secured together to form an integral structure. Alternatively, the diaphragm segments 25 may be cast as an integral structure and then machined into the final exact 60 segments. Other manufacturing methods will be obvious to those skilled in the art. It will also be obvious that the nozzle diaphragm 20 may have various numbers of segments 25. For example, the nozzle diaphragm 20 may be comprised of twelve 30 segments instead of the six 60 segments illustrated; it has been found, however, that it is both convenient and practical to use six 60 segments as illustrated. In general, any number of segments may be used so long that the total number of vanes is divisible by that number; this assures that all segments have an equal number of vanes.

The segments 25 are formed with the openings 33, 34 and 35 at a definite radius R1 from the center of curvature of the segments. As shown by FIGURE 4, the vanes 2S of each diaphragm segment 25 are secured to the outer shroud 26 and the inner shroud 27 such that the flow areas proportional to distance T between adjacent vanes are equal. Since the tangential spacing X between adjacent vanes 2S is in turn proportional to the throat spacing T, equal flow areas between adjacent varies 2S are assured by making the axial spacing X between adjacent varies 25 equal. The outer shroud 26 and the inner shroud 27 of each segment 25 extend circumferentially beyond the end vanes of the segments tangential distances Y and Z on opposite ends of the segment. There is no prescribed relationship between the magnitudes of distances Y and Z except that their total must be equal to the distance X. It is thus obvious that the flow areas be tween all vanes 28 of the nozzle diaphragm 20, including the flow area between the end vanes of adjacent segments 25, are equal when all segments 25 are in abutting relationship. Assuming stress free expansion and contraction, the above statement is valid for any temperature at which the segments 25 may be placed in abutting relationship.

Turning back to FIGURES 1 and 2, a support cone 40 is secured to the inner wall 17 by suitable means such as circumferentially spaced bolts 41. The support cone 40 has a series of openings 42 at a radius R2 from the axis of the engine, the circumferential spacing between the openings 42 being the same as the spacing between the openings 33, 34 and 35 of the diaphragm segments 25. The segments 25 are placed in the gas turbine engine with openings 33, 34 and 35 aligned with respective ones of the openings 42. A first bolt 43 is then passed through each opening 33 and the associated opening 42. The bolt 43 and the openings 33 and 42 form a snug fit, i.e., the bolt 43 is said to be body-bound, so that the circumfer ential center of the segment 25 is held in a fixed position. Similar bolts 44 and 45 are loosely received in the openings 34 and 35 so that the ends of the diaphragm segments 25 are free to expand and contract circumferentially relative to their fixed centers. The reason for making the openings 34 and 35 larger than opening 33 will now be apparent. If it is desired to make openings 34 and 35 the Same size as opening 33, bolts 44 and 45 must be smaller in diameter than bolt 43. If there is a tendency in practice for the segments 25 to pivot about the bolts 43, the openings 33 and 34 may be formed as circumferentially elongated slots instead of circular holes.

With the segments 25 mounted at the radius R2 from the axis of the engine, there is a clearance C between adjacent segments 25 since R2 is greater than R1. The radii R1 and R2 and the clearance C are chosen such that the segments 25 will expand into abutting relationship at the normal operating temperature of the nozzle diaphragm 20. as discussed previously, the How areas between all adjacent vanes 2S of the nozzle diaphragm 20 will thus be equal at the normal operating temperature.

The particular choices of R1, R2, and, therefore, C depend on a number of factors which must be determined with respect lto the particular engine on which the nozzle diaphragm 20 is to be used. For example, the particular material from which the nozzle diaphragm segments 25 are formed must be considered since different materials have different coefficients of thermal expansion. The normal operating temperature of the nozzle diaphragm and the temperature at which the segments 25 are assembled must also be considered. Similarly, the amount of expansion of the support cone 40 must also be taken into consideration; this expansion is generally relatively slight since the support cone 40 is subjected to relatively cool compressed air in the space 16 and not to the hot combustion products.

In a particular engine utilizing this invention, the nozzle diaphragm segments were formed of Inco 713C having a coeticient of thermal expansion of 8.15 X-6. So that the segments 25, assembled at a temperature of 70 F., would abut at the normal operating temperature of 1400 F., R1 was 3.474 inches and R2 was 3.490 inches, thus giving a clearance C of .017 inch between adjacent segments 25.

The supporting arrangement described above locates the circumferential centers of the segments 25 in a ixed position and allows circumferential expansion and contraction of the ends of the diaphragm segments. The support means for locating the nozzle diaphragm axially will now be described. A circumferential liange 46 extends radially inward from the casing 10 at the downstream face of the lianges 31 which extend outwardly from shroud members 26. The high pressure products of combustion entering the nozzle diaphragm 20 hold the anges 31 in contact with the flange 46. Support cone 40 engaging anges 32 helps locate the nozzle diaphragm 20 axially.

Plates 36 and 37 overlap the abutting joints between the shroud members of adjacent shroud segments 25. These plates prevent leakage of high pressure air from the combustion space 16 through the joints to the relative low pressure area adjacent the trailing edge 30 of the vanes 28.

It is thus seen that a nozzle diaphragm constructed in accordance with this invention has equal liow area between all vanes at its normal operating temperature. It also will be obvious that the invention has particular application to any stator assembly which is subjected to substantial changes in temperature during normal operation.

It will be understood that the invention is not limited to the specic details of the construction and arrangement of the particular embodiment illustrated and disclosed herein. It is therefore intended to cover in the appended claims all such changes-and modications which may occur to those skilled in the art without departing from the true spirit and scope of the invention.

What is claimed as new and desired to secure by Letters Patent of the United States is:

1. For use in a gas turbine engine having a casing and a turbine wheel rotatably mounted about an axis therein, a segmented annular nozzle diaphragm for supplying hot gases to said turbine wheel, said diaphragm comprised of a plurality of arcuate diaphragm segments each having an arcuate inner shroud member, an arcuate outer shroud member, a plurality of vanes radially positioned between said shroud members and secured thereto, said vanes being equally spaced circumferentially so as to deiine equal flow areas between adjacent ones of said vanes, a first arcuate mounting flange extending radially inward from said inner shroud member, and a second arcuate mounting iiange extending radially outward from said outer shroud member, said inner and outer shroud members extending circumferentially beyond the end vanes of said segments, the circumferential lengths of said extension being such that the llow area between the end vanes of two abutting segments is equal to the ow areas between adjacent vanes of each of said segments at any temperature, first support means engaging 'said iirst and second mounting flange of each of said segments to locate said segments axially within said gas turbine engine, and second support means engaging said first mounting flange of each of said segments to locate said segments circumferentially and radially within said gas turbine engine, said second support means locating the circumferential center of each of said segments in a fixed position and permitting the ends of said segments to expand and contract circumferentially relative to said centers in response to changes in the operating temperature of said diaphragm, the circumferential spacing between adjacent segments being such that the ends of said segments expand into abutting relationship at the normal operating temperature, the flow areas between the end vanes of abutting segments thereby being equal to the areas between adjacent vanes of each of said segments at the normal operating temperature.

2. A segmented annular nozzle diaphragm as defined by claim l, each of said irst mounting anges having a lirst opening at the circumferential center of said associated segment and second and third openings circumferentially spaced on opposite sides of said irst opening, and said second support means for each of said segments comprising a iirst member snugly received in said rst opening and second and third members loosely received in said second and third openings respectively.

3. A segmented annular stator assembly for use in a high temperature fluid flow machine comprised of at least two arcuate segments each having an arcuate inner shroud member, an arcuate outer shroud member, and a plurality of vanes radially positioned between said shroud members and secured thereto, said vanes being equally spaced circumferentially so as to deiine equal ow areas between adjacent ones of said vanes, said inner and outer shroud members extending circumferentially beyond the end vanes of said segments, and means supporting each of said segments in said fluid llow machine in circumferentially spaced relationship to adjacent ones of said segments, said supporting means locating yone portion only of each of said `segments 4in a lixed position and leaving the ends of each of said segments free to expand and contract circumferentially relative to said fixed portions in response to changes in the operating temperature of the stator assembly, the circumferential spacing between adjacent segments being such that the portions of said shroud members extending circumferentially beyond the end vanes of adjacent ones of said segments expand into abutting relationship at the normal high operating temperature, the total circumferential lengths of adjacent ones of said extensions being such that the flow area between the end vanes of two abutting segments is equal to the flow areas between adjacent vanes of each of said segments at the normal operating temperature, whereby the flow areas between all vanes of said annular stator assembly are equal at the normal high operating temperature.

4. For use in a high pressure gas turbine engine having a casing and a turbine wheel rotatably mounted about an axis therein, a segmented annular nozzle diaphragm for supplying hot gases to said turbine wheel, said diaphragm comprised of a plurality of arcuate diaphragm segments each having an arcuate inner shroud member, an arcuate outer shroud member, and a plurality of vanes radially positioned between said shroud members and secured thereto, said vanes being equally spaced circumferentially so as to define equal flow areas between adjacent ones of said vanes, said inner and outer shroud members extending circumferentially beyond the end vanes of said segments, rst support means engaging each of said segments to locate said segments axially within said high temperature gas turbine engine, and second support means only engaging each of said segments to locate said segments circumferentially and radially within said gas turbine engine, said second support means fixing only the circumferential center of each of said segments in a fixed position and leaving the ends of each of said segments free to expand and contract circumferentially relative to said centers in response to changes in the operating temperature of said diaphragm, the circumferential spacing between adjacent segments being such that the portions of said shroud members extending circumferentially beyond the end vanes of adjacent ones of said segments expand into abutting relationship at the normal high operating temperature, the total circumferential lengths of adjacent ones of said extensions being such that the iiow area between the end vanes of two abutting segments is equal to the flow areas between adjacent vanes of each of said segments at the normal high operating temperature, whereby the fiow areas between all vanes of said annularnozzle diaphragm are equal at the normal operating temperature.

5. For use in a high temperature gas turbine engine having a casing and a turbine wheel rotatably mounted about an axis therein, a segmented annular nozzle diaphragm for supplying hot gases to said turbine Wheel, said diaphragm comprised of a plurality of arcuate diaphragm segments each having an arcuate inner shroud member including a mounting ange depending therefrom, an arcuate -outer shroud member, a plurality of vanes radially positioned between said shroud members and secured thereto, said vanes of each segment being equally spaced circumferentially so as yto define equal flow areas between adjacent ones of said vanes, an arcuate mounting flange secured to `one of said shroud members, said inner and outer shroud members extending circumferentially beyond the end vanes of each of said segments, first support means engaging each of said segments to locate said segments axially within said high temperature gas turbine engine, and second support means engaging the mounting flange of each of said segments to locate said segments circumferentially and radially within said gas turbine engine, said second support means fixing only the circumferential center of each of said segments in a fixed position and leaving the ends of said segments free to expand and contract circumferentially relative to said centers in response to changes in the operating temperature of said diaphragm, the circumferential spacing between adjacent segments being such that the portions of said shroud members extending circumferentially beyond the end vanes of adjacent ones of said segments expand into abutting relationship at the', normal high operating temperature, .the total circumferential lengths of adjacent ones of said extensions being such that the fiow area between the end vanes of vtwo abutting segments is equal to the fiow areas between adjacent vanes of each of said segments at the normal high operating temperature, whereby the flow areas between all vanes of said annular nozzle diaphragm are equal at the normal operating temperature.

6. For use in a high temperature gas turbine engine having a casing and a turbine Wheel rotatably mounted about an axis therein, a segmented `annular nozzle diaphragm for supplying hot gases to said turbine wheel, said diaphragm comprised of a plurality of arcuate diaphragm segments each having an arcuate inner shroud member, an arcuate outer shroud member, a plurality of vanes radially positioned between said shroud members and secured thereto, said vanes being equally spaced circumferentially so as to define equal flow areas between adjacent ones of said vanes, an arcuate mounting tiange secured to one of said shroud members, each of said mounting lianges having a first opening at the circumferential center of the associated segment and second and third openings circumferentially spaced on opposite sides of said first opening, said inner and outer shroud members extending circumferentially beyond the end vanes of said segments, first support means engaging each of said segments to locate said segments axially within said gas turbine engine, and second support means comprising a first member snugly received in the first opening of each of said lianges and second and third member loosely received in said second and third openings, respectively, to locate said segments circumferentially and radially within said high temperature gas turbine engine, said second support means locating the circumferential center of each of said segments in a fixed position and leaving the ends of each of said segments free to expand and contract circumferentially relative to said centers in response to changes in the temperature of said diaphragm, the circumferential spacing between adjacent segments being such that the portions of said shroud members extending circumferentially beyond the end vanes of adjacent ones of said segments expand into abutting relationship at the `normal high operating ternperature, the total circumferential lengths of adjacent ones of said extensions being such that the liow area between the end vanes of two abutting segments is equal to the flow areas between adjacent vanes of each of said segments at the normal operating temperature, whereby the liow areas between all vanes of said annular nozzle diaphragm are equal at the normal operating temperature.

References Cited in the file of this patent UNITED STATES PATENTS 2,772,069 Hockert et al. Nov. 27, 1956 3,069,135 Welsh Dec. 18, 1962 FOREIGN PATENTS 615,110 Canada Oct. 7, 1957 

1. FOR USE IN A GAS TURBINE ENGINE HAVING A CASING AND A TURBINE WHEEL ROTATABLY MOUNTED ABOUT AN AXIS THEREIN, A SEGMENTED ANNULAR NOZZLE DIAPHRAGM FOR SUPPLYING HOT GASES TO SAID TURBINE WHEEL, SAID DIAPHRAGM COMPRISED OF A PLURALITY OF ARCUATE DIAPHRAGM SEGMENTS EACH HAVING AN ARCUATE INNER SHROUD MEMBER, AN ARCUATE OUTER SHROUD MEMBER, A PLURALITY OF VANES RADIALLY POSITIONED BETWEEN SAID SHROUD MEMBERS AND SECURED THERETO, SAID VANES BEING EQUALLY SPACED CIRCUMFERENTIALLY SO AS TO DEFINE EQUAL FLOW AREAS BETWEEN ADJACENT ONES OF SAID VANES, A FIRST ARCUATE MOUNTING FLANGE EXTENDING RADIALLY INWARD FROM SAID INNER SHROUD MEMBER, AND A SECOND ARCUATE MOUNTING FLANGE EXTENDING RADIALLY OUTWARD FROM SAID OUTER SHROUD MEMBER, SAID INNER AND OUTER SHROUD MEMBERS EXTENDING CIRCUMFERENTIALLY BEYOND THE END VANES OF SAID SEGMENTS, THE CIRCUMFERENTIAL LENGTHS OF SAID EXTENSION BEING SUCH THAT THE FLOW AREA BETWEEN THE END VANES OF TWO ABUTTING SEGMENTS IS EQUAL TO THE FLOW AREAS BETWEEN ADJACENT VANES OF EACH OF SAID SEGMENTS AT ANY TEMPERATURE, FIRST SUPPORT MEANS ENGAGING SAID FIRST AND SECOND MOUNTING FLANGE OF EACH OF SAID SEGMENTS TO 